This invention relates to systems and methods for noninvasively measuring hemodynamic access, access recirculation and blood flow measurements during hemodialysis. More particularly, the present invention relates to noninvasive spectrophotometric systems and methods for quantitatively measuring the shunt (access) recirculation, the access blood flow rate, the dialysis machine blood flow rate and the volumes of priming fluids required by the hemodialysis tubing lines.
Modern medical practice utilizes a number of procedures and indicators to assess a patient""s condition especially in the dialysis setting. Hemodialysis is a process wherein an artificial kidney is required to function in the place of the patient""s normal kidney in order to remove certain biologic waste products. When the human kidney no longer functions correctly removing waste products such as urea, potassium, and even excess water, blood must be removed from the patient via blood tubing lines and filtered through an artificial kidney or dialyzer. In this process blood is passed through the dialyzer, cleansed, then returned to the normal circulatory system of the patient. Access to the patient""s circulatory system is achieved through the use of a surgically implanted shunt or fistula. This xe2x80x9caccess sitexe2x80x9d is typically located in the arm, leg, or neck of the patient. Typically needles are placed into this xe2x80x9caccessxe2x80x9d in such a way as to facilitate the easy removal of blood on the xe2x80x9carterialxe2x80x9d or upstream side of the dialyzer and typically return the purified blood downstream of the first needle placement on the xe2x80x9cvenousxe2x80x9d side. Unfortunately, in many cases the fistula, or shunt, will clot or xe2x80x9cstenosxe2x80x9d over time. This results in decreased blood flow through the access which ultimately necessitates either angioplasty or a surgical replacement of the shunt. As the shunt ceases or xe2x80x9cclots offxe2x80x9d part of the purified dialyzed blood is forced to flow back into the arterial withdrawal site and, hence, recirculates only to be dialyzed again; this is termed xe2x80x9caccess recirculationxe2x80x9d. As this recirculation of purified blood continues, the rest of the patient""s circulating blood is not adequately cleansed and, hence, an inadequate delivery of the dialysis dosage is provided to the patient.
Therefore, because of the possibility of inadequate dialysis dosage due to this direct recirculation of purified blood back to the withdrawal site, various techniques and methods have been designed to determine:
1) The degree or percentage of access recirculation;
2) The actual blood flow rate in the shunt per se; and
3) The dialyzer blood flow rate itself.
Medical professionals desire to know these three parameters not merely qualitatively, but quantitatively in order to determine the presence and degree of clotting or stenosis. These parameters are desired to predict when the access is beginning to fail and to determine the need for access revision by surgery. Blood flow, Q, measured by the so-called Ficke dilutional techniques, has been described by A. C. Guyton, Textbook of Medical Physiology, Sixth Edition, pg. 287, 1981, wherein Q equals the volume of the injected diluent divided by the mean concentration of the diluent times the duration of the passage of the diluent through the vessel. A dilution curve is obtained by continuously monitoring changes in a given physical parameter of the blood over the time period of the injection. The change in the concentration of either the diluent (or the media) is measured over time.
Hester, R. L. et al., American Journal of Kidney Disease 20:6, 1992, pp. 598-602, have shown that when the dialyzer blood lines are reversed, enhanced blood recirculation occurs. Krivitski, in European patent application number WO9608305A1, indicates that blood line reversal (causing forced recirculation) allows for the determination of the actual blood flow in the shunt.
One method of measuring access blood flow utilizes color coded duplex sonography. However, this technique is expensive. It involves highly trained professionals and the measurements suffer from operator error. The limitations due to variations in the blood vessel diameter and even the Doppler flow angle complicate this measurement.
Another method involves injection of a saline solution intravenously and recording optical detecting the change in the intensity of light passed through a conduit at a point upstream from the injection point (U.S. Pat. No. 5,312,550).
Another technique involves injecting saline boluses into the arterial and venous dialyzer tubing lines and measuring the change of ultrasound velocity (U.S. Pat. No. 5,453,576). This technique is sensitive to changes in temperature, plasma protein levels, and other intrinsic factors that change the density of the blood. Of more significance, however, is that the measurements of the absolute ultrasound velocity changes are influenced not only by the intrinsic blood factors, but also by the unknown mechanical properties of the tubing line per se. In order to compensate for those intrinsic and extrinsic physical problems an additional calibration injection of saline is generally required in the opposite tubing line, whether arterial or venous, thereby producing relative changes in the degree of dilution that occurs due to the saline bolus. Hence, the unknown ultrasound characteristics of the tubing line and other physical, dimensional characteristics can be minimized.
The present standard measurement for access recirculation requires three blood urea nitrogen samples from the patient while on dialysis. However, in addition to the blood samples required from the patient, nursing time, laboratory costs, and appropriate blood flow rates must be maintained during the actual sampling procedure to assure correct urea nitrogen measurements.
Thus, there remains a need for systems and methods for noninvasively and quantitatively determining a patient""s hemodynamic access blood flow and blood recirculation parameters.
Thus, it is an object of the present invention to provide a system and method for noninvasive access hemodynamic monitoring that requires minimal nursing time and no discreet blood sampling.
It is another object of the present invention to provide a system and method for the display of both immediate and continuous visual information regarding the saline dilutional hemodynamic access data.
It is yet another object of the present invention to provide repeatable and reliable systems and methods for the noninvasive determination of the hemodynamic access flow properties under varying conditions including: different ultrafiltration rates, patient postures, tubing types and dimensions, and even different dialyzer membranes and dialysis delivery systems.
Another object of the present invention is to provide a means and method of quantitatively determining the volumetric blood flow rate actually passing through the dialyzer, Qi.
Another object of the present invention is to present the dilutional concentration-time curves to the operator by visual, real-time display means.
Still another object of the present invention is to provide a system and method which can provide immediate and quantitative determination of the actual volume of fluid necessary to prime the dialyzer circuit.
It is likewise another object of the present invention to provide a system and method for determining the access blood flow and access recirculation that does not require the injection of saline. For example, by changing the ultrafiltration rate (UFR) or dialyzer blood flow rate. It is another object of the present invention to provide a system and method for measuring dialyzer blood flow parameters.
These and other objects and advantages of the invention will become more fully apparent from the description in the claims which follow or may be learned by the practice of the invention.
In one aspect of the present invention, access recirculation in a shunt is determined quantitatively by a method in which a standard solution, such as a saline solution, is injected into the patient""s bloodstream at a point upstream of the shunt. At a point in the access line, a photometric measurement is conducted of the change in hematocrit (xcex94H) with respect to time. Electronic circuitry receives signals from the detector and compares the integrated area of xcex94H with respect to time of the standard solution initially flowing through the access and of the recirculated solution and provides a nearly instantaneous display of the amount of access recirculation.
In another aspect of the present invention, the access recirculation and/or access blood flow are quantitatively determined without injecting a solution into the bloodstream. In this aspect the extent of access recirculation and/or access blood flow is determined quantitatively by a method in which the dialyzer blood flow rate or the ultrafiltration rate (UFR) is changed and the corresponding change in concentration of a blood constituent is measured. In this technique, the concentration of a blood constituent is measured as a function of dialyzer blood flow rate or UFR and electronic circuitry converts these measurements into quantitative determinations of access recirculation and/or access blood flow that can be displayed nearly instantaneously. In a preferred embodiment the measured blood constituent is red blood cells.